A control system includes an electronic control unit and a number of sensors, which are interconnected by means of a current-controlled bus. The control system in particular can be installed on board of a motor vehicle, and the sensors can record parameters, which are forwarded to or processed by the control unit for the purpose of operating the motor vehicle. The control unit supplies a predefined quiescent current through a bus line of the current-controlled bus, and one of the sensors modifies this current in such a way that a digital transmission of data between the sensor and control unit is possible. Known current-controlled buses, for example, include PAS4 and PSI5.
For instance, a high current flow could correspond to a digital 1 and a low current flow to a digital 0. The control unit samples the current and converts it into a digital message of the sensor. At predefined time intervals, a synchronization pulse is generated on the bus. The control unit may include a separate current controller for this purpose, which supplies the synchronization current. The synchronization current may exceed an operating current of the current-controlled bus. If multiple sensors are connected to the bus, then a sensor for the data transmission may be selected by means of the synchronization pulse. In addition, a time synchronization of the sensors with the control unit is able to take place to facilitate the data transmission. Such an operation, which is able to operate without a separate timing circuit, is also referred to as an asynchronous operation.
Although only one of the sensors modulates the current flowing through the bus line at each instant, this current may also be affected by the other sensors, for example by their quiescent current withdrawal. In addition, the flowing current may vary on account of external influences, such as electromagnetic irradiation, thermal effects or voltage fluctuations of a voltage supply to which the control unit or one of the sensors is connected. To ensure correct functioning of the control unit or to calibrate the control unit, it is common practice to connect the control unit to a bus and one or more sensor(s) and to simulate different influences prior to the installation in the control system. The bus and the sensors may include real components or copies of real components.
The testing or calibration of the control unit at the described structure is involved and time-intensive. Especially when each control unit must be calibrated or tested individually, the manufacturing costs of the electronic control unit or the control system may be higher. It is an object of this invention to provide a simplified test structure and a test method for checking the control unit, which allow easier and less cost-intensive checking of the control unit. The present invention achieves this objective by a control unit and a method having the features of the respective independent claims. In addition, a computer program product is provided for achieving the objective.